Create image processing apps powered by Apple silicon

10:53 - Memoryless attachments

let textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(…)
let outputTexture = device.makeTexture(descriptor: textureDescriptor)

textureDescriptor.storageMode = .memoryless
let tempTexture = device.makeTexture(descriptor: textureDescriptor) 

let renderPassDesc = MTLRenderPassDescriptor()
renderPassDesc.colorAttachments[0].texture      = outputTexture
renderPassDesc.colorAttachments[0].loadAction   = .dontCare
renderPassDesc.colorAttachments[0].storeAction  = .store
renderPassDesc.colorAttachments[1].texture      = tempTexture
renderPassDesc.colorAttachments[1].loadAction   = .clear
renderPassDesc.colorAttachments[1].storeAction  = .dontCare

let renderPass = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDesc)

12:25 - Uber-shaders impact on registers

fragment float4 processPixel(const constant ParamsStr* cs [[ buffer(0) ]])
{
  if (cs->inputIsHDR) {
    // do HDR stuff
  } else {
    // do non-HDR stuff
  }
  if (cs->tonemapEnabled) {
    // tone map
  }
}

13:32 - Function constants for Uber-shaders

constant bool featureAEnabled[[function_constant(0)]];
constant bool featureBEnabled[[function_constant(1)]];

fragment float4 processPixel(...)
{
  if (featureAEnabled) {
    // do A stuff
  } else {
    // do not-A stuff
  }
  if (featureBEnabled) {
    // do B stuff
  }
}

23:02 - Image processing filter graph

typedef struct
{
    float4 OPTexture        [[ color(0) ]];
    float4 IntermediateTex  [[ color(1) ]];
} FragmentIO;

fragment FragmentIO Unpack(RasterizerData in [[ stage_in ]],
                           texture2d<float, access::sample> srcImageTexture [[texture(0)]])
{
    FragmentIO out;
    
    //...
                         
    // Run necessary per-pixel operations
    out.OPTexture       = // assign computed value;
    out.IntermediateTex = // assign computed value;
    return out;
}

fragment FragmentIO CSC(RasterizerData in [[ stage_in ]], FragmentIO Input)
{
    FragmentIO out;

    //...    
    
    out.IntermediateTex = // assign computed value;
    return out;
}